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Relationship between the oxygen uptake efficiency plateau and the individual anaerobic threshold in endurance swimmers

Jailton G Pelarigo1,2,3, Athanasios Dalamitros4, Ana C Sousa2, Ricardo J Fernandes2,3, Camila Coelho Greco5, João Paulo Vilas-Boas2,3 1The Capes Foundation, Ministry of Education of Brazil, 2Faculty of Sport/CIFI2D, University of Porto, Portugal, 3LABIOMEP, University of Porto, Portugal, 4School of Physical Education & Sport Sciences, Aristotle University of Thessaloniki, Greece, 5São Paulo State University, Brazil

Keywords: oxygen uptake efficiency, velocity at individual anaerobic threshold, swimming

Abstract Introduction. The oxygen uptake efficiency slope (OUES) has been proposed as a valid index for the objective estimation of cardiopulmonary function during submaximal laboratory testing (Baba et al. 1996). OUES is strongly correlated with maximal oxygen uptake (V�O2max) and has been observed to reach its highest and leveling off values (plateau—OUEP) near the anaerobic threshold (AT) in patients with cardiorespiratory disease and normal subjects (Sun, Hansen & Stringer 2012). However, OUES and OUEP have never been studied in highly trained athletes, particularly swimmers. The purpose of this study was to compare the velocity and oxygen uptake efficiency (OUE) values obtained during OUEP and individual anaerobic threshold (IAnT) in well trained swimmers.

Methods. Eight female endurance swimmers (17.5 ± 1.9 yrs, 1.71 ± 0.06 m, 62.1 ± 6.2 kg) performed an intermittent incremental swimming step test (7 x 200 m, with increments of 0.05 m·s-1 and 30 s intervals). OUES was calculated by the ratio of oxygen uptake and minute ventilation. The IAnT was

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determined by the velocity vs. lactate curve modeling method. ANOVA for repeated measures and regression analysis were performed to test differences between methods (p<0.05).

Results. Similar velocity (1.20 ± 0.05 vs. 1.22 ± 0.05 m.s-1) and OUE values (43.9 ± 5.83 vs. 42.9 ± 5.8 mL V�O2.L V�E

-1) were obtained during OUEP and IAnT calculated intensities, respectively. Regarding the Passing & Bablok regression analysis and the Pearson’s coefficient of determination, velocity (Intercept A= -0.096, Slope B= 1.071, R2= 0.638, p<0.017) and OUE values (Intercept A= -5.360, Slope B= 1.154, R2= 0.875, p<0.001) obtained both at the OUEP and at the IAnT were highly correlated.

Conclusion. These findings suggest that OUEP has a practical application in swimming as a non-invasive submaximal index closely related to the IAnT in well-trained female endurance swimmers.

Acknowledgments. This research was supported by grants from the Capes Foundation, Ministry of Education of Brazil (BEX: 0536/10-5), and Project PTDC/DES/101224/2008 (FCOMP-01-0124-FEDER-009577).

Introduction Several methods have been used to assess aerobic endurance, while the measurement of maximal oxygen uptake (V�O2max) is the most objective and widely used. Besides V�O2max, other parameters, such as the anaerobic threshold (AT) and swimming economy are recognised to be important in the prediction of performance, especially in long-distance events (Bosquet, Leger & Legros 2002).

The oxygen uptake efficiency slope (OUES), expressing the ratio between oxygen uptake to minute ventilation, is considered to be a valid sub-maximal index for the measurement of cardiorespiratory fitness during laboratory testing (Baba, et al. 1996). The assessment of this index requires no maximal exercise and is significantly correlated with relevant exercise parameters, such as the peak and maximal oxygen uptake and the ventilatory threshold (Akkerman et al. 2010). Furthermore, OUES seems to be influenced by anthropometric variables, but not by the duration of the testing procedure (Baba, et al. 1996). Studies conducted with health subjects and patients with cardiorespiratory disease showed that OUE values reach a plateau (OUEP) near the anaerobic threshold. Interestingly, OUEP is considered to be more reproducible and less variable compared to OUES (Sun et al. 2012).

Meanwhile, the AT detected through blood lactate concentration values (IAnT) is presented as one of the most valid and reliable testing procedures in swimming to monitor training adaptations, evaluate the aerobic profile and prescribe training intensity (Morais et al. 2006; Pyne, Lee & Swanwick 2001). Complementary, the velocity corresponding to the IAnT is more strongly correlated with distance performance than V�O2max (Bassett & Howley 2000).

To date, no study has attempted to examine the relationship between OUEP and IAnT during field conditions in well trained swimmers. Thereby, the purpose of this study was to compare the swimming velocities and OUE values obtained during the OUEP and IAnT intensities in well trained swimmers.

Methods Eight female endurance swimmers (age 17.5 ± 1.9 yrs, height 1.71 ± 0.06 m, body mass 62.1 ± 6.2 kg and percentage of body fat 16.4 ± 2.6%) volunteered to participate in the study, giving their written informed consent before participation. In addition, swimmers below the age of 18 yrs provided written parental consent. The participants had at least seven years of experience as competitive swimmers and their best 400 m front-crawl performance corresponded to 87.4 ± 3.5% of the 2013 25 m pool world record.

The testing sessions were performed in a 25 m indoor swimming pool, after a standard warm-up of 1000 m at moderate self-paced swim and under the same pool conditions (27-280C). Swimmers were instructed to refrain from intense training sessions at least 24 h before testing.

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Swimmers performed an intermittent and incremental front-crawl protocol, with increments of 0.05 m.s-1 and 30 s rest intervals between each 200 m steps to assess IAnT and detect the swimming velocities associated with the OUEP. The predetermined velocity of the last step was calculated considering the best performance of the 400 m front-crawl race minus seven increments of velocity (Cardoso et al. 2003; R. J. Fernandes et al. 2006). Swimmers were advised to use in-water starts and open turns, without underwater gliding.

The swimming velocity (SV) was set and controlled using a visual underwater pacer with flashing lights on the bottom of the pool (GBK-Pacer, GBK Eletronics, Aveiro, Portugal) (Fernandes, Sousa, Machado & Vilas-Boas 2011); the lights were located 2.5 m apart along the bottom of the 25 m pool.

The V�O2 and V�E were measured by a telemetric portable gas analyzer (K4 b2, Cosmed, Italy), connected to the swimmer by a low hydrodynamic resistance respiratory snorkel and valve system (New AquaTrainer®, Cosmed, Italy), previously validated (Baldari et al. 2013). The equipment was calibrated before each test for V�E with a 3 L calibrated syringe and the O2 and CO2 analyzers with standard calibration gases. The values of gas exchange were measured breath-by-breath during the test and averaged every 5 s. Heart rate (HR) was recorded continuously (Polar Electro, Kempele, Finland) throughout the test.

Collection of blood samples (BLa) were performed in the first 30 s after each step, at the earlobe using a portable lactate analyzer (Lactate Pro, Akray, Japan). The IAnT was determined by the velocity vs. lactate curve modeling method. The lactate increase inflexion point was considered to be the interception point between linear and exponential regressions to determine the exact velocity where BLa increased exponentially (Machado, Almeida, Morais, Fernandes & Vilas-Boas 2006). The OUES was calculated by the ratio of oxygen uptake and minute ventilation. The OUE plateau (OUEP) was considered as the highest consecutive measurements of oxygen uptake (V�O2) / minute ventilation (V�E) values briefly stabilised near the AT, before declining due to hyperventilation stimulated by the excess [H+] and metabolic acidosis (Sun et al. 2012). In the case a swimmer did not attain the maximal velocity and/or exhaustion with the pre-defined steps, one more step was used.

Data are presented as mean (±SD). Standard statistical assumptions were checked before the analysis. ANOVA one-way for repeated measures and Passing & Bablok regression analysis (MedCalc Statistical Software, Belgium) were conducted to compare SV and OUE values obtained during OUEP and IAnT calculated intensities, complemented with Bonferroni correction and post-hoc test. The Pearson’s determination coefficient (R2) was used. Statistical significance level was set at p ≤ 0.05.

Results Table 1 presents the mean (SD) SV and OUE values obtained at the OUEP and IAnT intensities.

Table 1 Mean (SD) values for SV and OUE values obtained during the OUEP and IAnT intensities (n=8)

SV (m.s-1) OUE (mL V�O2. L V�E-1)

OUEP 1.20 (0.05) 43.9 (5.8)

IAnT 1.22 (0.05) 42.9 (5.8)

According to Table 1, similar velocity (F1,7 = 2.635, p < 0.149, ήp2 = 0.273) and OUE values (F1,7 = 1.913,

p < 0.209, ήp2 = 0.215) were observed both for OUEP and IAnT calculated intensities. Table 2 presents

the mean (SD) sub-maximal BLa, HR and V�O2 values corresponding to the IAnT.

Table 2 Mean (SD) values for the sub-maximal physiological variables corresponding to the IAnT (n=8)

BLa (mmol.L-1) HR (b.min-1) V�O2 (mL.min-1.kg-1)

1.50 (0.47) 171.76 (5.62) 44.42 (4.27)

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The Passing & Bablok analysis and the Pearson’s determination coefficient showed that swimming velocity and OUE mean values obtained through the OUEP and IAnT intensities were highly correlated (p ≤ 0.05) (Table 3). Figure 1 and 2 present the Passing-Bablok regression analysis and Bland-Altman plot, respectively, determined between OUES and IAnT intensities concerning the SV (Left Panel) and OUE (Right Panel) values.

In Table 3, the coefficient of determination (R2), p value and regression equation variables for the comparison between the OUEP and IAnT intensities for SV and OUE values are presented.

Table 3 Comparison between the OUEP and IAnT intensities for SV and OUE values

OUEP vs. IAnT

Parameters R2 p value Slope B Intercept A

SV (m.s-1)

0.638* 0.017 1.071 (0.339 to 2.128) -0.096 (-1.404 to 0.786)

OUE (mL O2. L V�E-1)

0.875* 0.001 1.155 (0.673 to 2.351) -5.360 (-56.188 to 14.909)

*p <0.05.

Figure 1 Passing-Bablok regression analysis obtained during OUES and IAnT intensities regarding the SV (left panel) and the OUE values (right panel) (n=8)

Figure 2 Bland-Altman plot of the OUES and IAnT intensities regarding the SV (left panel) and the OUE values (right panel) (n=8)

Discussion The current study presents sub-maximal OUE values obtained in well-trained female endurance swimmers, as well as comparison between OUEP and IAnT intensities regarding both OUE and SV. The

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main findings indicate that SV as well as OUE values attained during OUEP and IAnT intensities are highly correlated and not significantly different, suggesting that they both refer to the same biophysical state of the swimmer.

Caution must be taken when comparing SV, BLa and HR mean values corresponding to the IAnT of our participants with those from other studies, due to the inconsistency regarding the methodology applied for the IAnT determination in swimming. Approaches usually include SV and HR values at: (i) the fixed 4 mmol·L-1 BLa, (ii) at the final step of the incremental test, (iii) during different testing procedures (i.e., 2 to 7 x 200 m step tests) or, (iv) include the mathematical approach to determine the individual IAnT (Altimari, Altimari, Gulak & Chacon-Mikahil 2007; Anderson, Hopkins, Roberts & Pyne 2006; Fernandes et al. 2010; Pyne, Anderson & Hopkins 2006). Nevertheless, Pyne et al. (2001) and Thanopoulos (2010) presented higher BLa values at the IAnT than those reported in this study (3.6 and 5.5 mmol·L-1 in world-ranked male/female and national level female swimmers, respectively). Similarly, in the latter study the SV values corresponding to the IAnT were higher than those presented here (1.45 vs. 1.22 m.s-1). At least partially, differences might be attributed to the performance level of the swimmers.

Sub-maximal OUE values presented in this study are in accordance with those reported by Akkerman, et al. (2010), despite the differences in the conditions used for exercise testing (cycle ergometer vs. free swimming) and the chronological age of the participants (12.9 ± 2.6 vs. 17.5 ± 1.9 yrs). Sun et al. (2012) showed that OUES is significantly influenced by age and body size.

To our knowledge, this is the first attempt to examine the practical application of the OUEP method by correlating and comparing OUE and SV values obtained during OUEP and a widely accepted field test, such as the IAnT, in well-trained swimmers. From a practical point of view, OUEP may be used to assess IAnT without using intrusive procedures. Furthermore, once OUES indicates ventilatory efficiency with regard to V�O2 (Akkerman, et al. 2010), the leveling off values of OUES at the intensity correspondent to the IAnT, implies that, at this particular intensity, a deleterious effect of exercise intensity is observed over the respiratory dynamics. OUES may be also used as a potential sub-maximal index of swimming economy, since the latter is considered to be an efficiency index, expressing the V�O2 required to maintain a given swimming velocity. Since distance swimming performance is significantly influenced by the V�O2max and the AT, the results obtained during this study can provide valuable information for designing training programs in swimmers. Future work should focus on examining the efficacy of the OUES and OUEP indeces in determining adaptations after a training period.

Acknowledgments This research was supported by grants from the Capes Foundation, Ministry of Education of Brazil (BEX: 0536/10-5), and Project PTDC/DES/101224/2008 (FCOMP-01-0124-FEDER-009577).

References Akkerman, M., van Brussel, M., Bongers, B. C., Hulzebos, E. H., Helders, P. J. & Takken, T. (2010). Oxygen uptake

efficiency slope in healthy children. Pediatr Exerc Sci, 22(3), 431-441.

Altimari, J. M., Altimari, L. R., Gulak, A. & Chacon-Mikahil, M. P. T. (2007). Correlations between anaerobic threshold determination protocols and aerobic performance in adolescent swimmers. Revista Brasileira de Medicina do Esporte, 13(4), 221e-226e.

Anderson, M., Hopkins, W., Roberts, A. & Pyne, D. (2006). Monitoring seasonal and long-term changes in test performance in elite swimmers. European Journal of Sport Science, 6(3), 145-154.

Baba, R., Nagashima, M., Goto, M., Nagano, Y., Yokota, M., Tauchi, N. & Nishibata, K. (1996). Oxygen uptake efficiency slope: a new index of cardiorespiratory functional reserve derived from the relation between oxygen uptake and minute ventilation during incremental exercise. J Am Coll Cardiol, 28(6), 1567-1572.

Baldari, C., Fernandes, R. J., Meucci, M., Ribeiro, J., Vilas-Boas, J. P. & Guidetti, L. (2013). Is the new AquaTrainer(R) snorkel valid for VO2 assessment in swimming? Int J Sports Med, 34(4), 336-344.

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Bassett, D. R., Jr. & Howley, E. T. (2000). Limiting factors for maximum oxygen uptake and determinants of endurance performance. Med Sci Sports Exerc, 32(1), 70-84.

Bosquet, L., Leger, L. & Legros, P. (2002). Methods to determine aerobic endurance. Sports Med, 32(11), 675-700.

Cardoso, C., Fernandes, R., Magalhaaes, J., Santos, P., Colaço, P., Soares, S., Vilas-Boas, J. P. (2003). Comparison of Continuous and Intermittent Incremental Protocols for Direct VO2max Assessment. In J. C. Chatard. (Ed.), Biomechanics and Medicine in Swimming IX (pp. 313-319). Saint-Étienne: Publications de l’Universií de Saint-Étienne.

Fernandes, R. J., Billat, V. L., Cruz, A. C., Colaco, P. J., Cardoso, C. S. & Vilas-Boas, J. P. (2006). Does net energy cost of swimming affect time to exhaustion at the individual’s maximal oxygen consumption velocity? J Sports Med Phys Fitness, 46(3), 373-380.

Fernandes, R. J., Sousa, M., Machado, L. & Vilas-Boas, J. P. (2011). Step length and individual anaerobic threshold assessment in swimming. Int J Sports Med, 32(12), 940-946.

Fernandes, R. J., Sousa, M., Pinheiro, A., Vilar, S., Colaço, P. & Vilas-Boas, J. P. (2010). Anaerobic Threshold Individualized Assessment in a Young Swimmer. The Open Sports Sciences Journal, 3, 134-136.

Machado, L., Almeida, M., Morais, P., Fernandes, R. & Vilas-Boas, J. P. (2006). Assessing the individual anaerobic threshold: the mathematical model. Paper presented at the Xth International Symposium of Biomechanics and Medicine in Swimming, Porto, Portugal.

Morais, P., Cardoso, C., Faria, V., Rocha, S., Machado, L., Fernandes, R. & Vilas-Boas, J. P. (2006). Oxygen uptake and ventilatory threshold in swimming. In J. P. Vilas-Boas, F. Alves & A. Marques (Eds.), Xth International Symposium of Biomechanics and Medicine in Swimming (pp. 130-132). Porto.

Pyne, D. B., Anderson, M. E. & Hopkins, W. G. (2006). Monitoring changes in lean mass of elite male and female swimmers. International Journal of Sports Physiology and Performance, 1(1), 14-26.

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Stroke mechanics profile and swimming economy during progressive VO2max test

Dalton M Pessôa Filho1, Joana F Reis2, Francisco Alves2, Camila C Greco1, Benedito S Denadai1 1São Paulo State University, UNESP, Brazil, 2CIPER – Faculty of Human Kinetics, University of Lisbon, Portugal

Keywords: crawl stroke, energy cost, aerobic assessment

Abstract Introduction: The relationshipsofdistance per stroke (Ds) and stroke rate (SR) with velocity (v)progression,over a range of swimming intensities within aerobic energy supply, did not evidence how Ds and SR slopes (Dsslope and SRslope, as well as, the crossing point (Cp) between them)change their profiles during maximal aerobic test, and what is the parameter of endurance capacity (among gas exchange threshold (GET), respiratory compensation point (RCP), maximal oxygen uptake (VO2max), and economy (e)) that correlates better to these changes.

Purpose: the aimed was to highlight the physiological responses associated to Ds and SR changes as swimming velocity increases. Even, analyze if Ds and SR are reliable indices to the control of training and/or improvements in aerobic pace.

Methods: Nine subjects performed a continuous incremental test (300m per stage) until volitional exhaustion. Eachstagewas designed by percentages of the maximal crawl velocity in 400m (%v400). VO2max, GET and RCP were examined. The velocities corresponding to VO2max (vVO2max), GET

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